Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
Of the two consular armies,
each of which numbered about 25,000 infantry and 1100 cavalry, one
was stationed in Sardinia under Gaius Atilius Regulus, the other at
Ariminum under Lucius Aemilius Papus. Both received orders to repair
as speedily as possible to Etruria, which was most immediately
threatened.
The Celts had already been under the necessity of leaving
a garrison at home to face the Cenomani and Veneti, who were allied
with Rome; now the levy of the Umbrians was directed to advance from
their native mountains down into the plain of the Boii, and to inflict
all the injury which they could think of on the enemy upon his own
soil.
The militia of the Etruscans and Sabines was to occupy the
Apennines and if possible to obstruct the passage, till the regular
troops could arrive. A reserve was formed in Rome of 50,000 men.
Throughout all Italy, which on this occasion recognized its true
champion in Rome, the men capable of service were enrolled, and stores
and materials of war were collected.